The present invention relates to a chopper device used in a folder for a web-fed rotary printing press, and more particularly to a chopper device therefor which half-folds a signature conveyed after having been subjected to parallel folding, in a direction perpendicular to the parallel folding direction.
In a web-fed rotary printing press, there is provided in association therewith a folder which cuts a web, i.e., a roll of printing sheet which has undergone a printing process, into sheet segments having a predetermined size and then folds the sheet segments. The folder is provided with a former device for half-folding a web which has not been subjected to a cutting process in the sheet width direction, a parallel folding device to cut, in the length direction, a web which has undergone former folding or a web which has been cut in the sheet width direction using a slitter and then folded into sheet segments in the length direction, a chopper device to further fold, in a direction perpendicular to the parallel folding direction, signatures which have been subjected to parallel folding, and an apparatus for conveying the sheet segments, or signatures.
The chopper device which is the subject matter of the present invention operates as follows. First, a front edge of a signature is conveyed, by a conveying belt after being subjected to parallel folding, into contact with a front lay, thereby stopping the signature. Next a thin plate-like chopper blade is lowered toward the centerline of the stopped signature to cause the signature to be seized between a pair of rotary rollers so as to half-fold the signature. The signatures which have been subjected to half-folding as described above are delivered between paddles of a rotating fan wheel. Thus, they turn around along with the fan wheel and are delivered onto a delivery conveyor. Then, they are conveyed therefrom and are stacked.
With a conventional chopper device used in a folder, the following problem occurs. The signature, which is struck at its centerline by the chopper blade and then seized between the rotary rollers to undergo folding, is held or retained by the conveying belt at the beginning of the folding. However, since the signature is released from being held by the conveying belt at the end of folding, edge portions of the signature will rapidly lower, thereby contacting both sides of the structure by which the chopper blade is fitted. This invites the possibility that the printed surface of the edge portions will be strained or broken, resulting in generation of waste printed sheets.